Integrate a complex Swift Package into your iOS app

In this blog post I help app developers to understand the terminology of a Swift Package and how to integrate a more complex structured Swift Package in an iOS application.

The simplest package structure, created by the swift package init command, consists of

• a package
  • with a single product (type: library)
    • using a single target (+ a test target)

The names of all those package/product/target is identical.

Let's look at a more complex example:

// swift-tools-version: 5.6
import PackageDescription

let package = Package(
    name: "Package2",
    products: [
        .library(name: "Package2LibA", targets: ["Package2TargetA"]),
        .library(name: "Package2LibB", targets: ["Package2TargetB"]),
    ],
    dependencies: [
        .package(path: "../Package1"),
    ],
    targets: [
        .target(
            name: "Package2TargetA",
            dependencies: [.product(name: "Package1Lib", package: "Package1")]),
        .target(
            name: "Package2TargetB",
            dependencies: [.product(name: "Package1Lib", package: "Package1")])
        )
    ]
)

This package (named Package2 here) offers two library products. Each product has its own target. Each target makes use of a library offered by a package dependency.

Let me start explaining the different building blocks from the view of an app developer.

• You want to use functionality from a package => you add the package to your Xcode project.

• You want to use a library => you add a library product to your app target in Xcode.

  

• Finally, when importing related code from the library => you are using the import <target/module> statement.

  

  In this example the module Package2TargetB offers a public struct API_B.

A Swift target is pretty much equal to a Swift module, so they are often used interchangeably. A module specifies a namespace and enforces access controls on which parts of that code can be used outside of the module.

I highly recommend reading the definition given by Jeremy David Giesbrecht in the Swift Forum. It speaks more to package developers.